The commercial polyalphaolefins (PAO) typically are dimers, trimers and tetramers of 1-octene, 1-decene and 1-dodecene and are typically made by a two-stage process described in U.S. Pat. No. 4,045,507. The PAO oligomerization process is carried out using boron trifluoride with a complex-forming co-catalyst. The multistage process can include two continuous stirred tank reactors in series. Generally 1-decene or 1-dodecene and the co-catalyst usually an alcohol such as 1-butanol are added to the first reactor. Boron trifluoride gas is maintained over the two reaction vessels to form the boron trifluoride-alcohol catalyst in the reactors.
The oligomer product prepared by such a two-stage process is a mixture of dimer, trimer, tetramer and a small amount of higher oligomers. The oligomers are hydrogenated and the primary products, trimer and tetramer, are distilled to make hydrocarbon products that have viscosities at 100° C. of 2 cSt, 4 cSt, 6 cSt and 8 cSt. The trimer is 4 cSt and the tetramer is 8 cSt. 6 cSt PAO is a mixture of trimer and tetramer that is readily available commercially.
Less used but also commercially available polyalpha olefins are 40 cSt and 100 cSt made by a different process.
Boron trifluoride combines in the first reactor with the co-catalyst that is commonly an alcohol to form a coordination compound that is catalytically active for the oligomerization reaction. These cationic catalysts are typically at 110° F. and are known to produce a significant amount of isomerization of the double bond in the alphaolefin before oligomerization, increasing the amount of branching on the hydrocarbon backbone. Isomerization branching also occurs on the hydrocarbon chains in the branches. Branching in the oligomers gives conventional PAO a broad boiling point distribution.